This invention relates to a buffer comprising a plunger and cylinder unit, the plunger being forced into the cylinder when a load is applied to the buffer whereby liquid is displaced from a compression chamber within the cylinder into a relatively low pressure reservoir through flow resisting means which provide dynamic resistance.
In practice, such a buffer, which is referred to in this description as a buffer of the kind referred to, includes resilient means such as a spring arrangement or an enclosed body of compressed gas which provides a recoil force opposing inward movement of the plunger with respect to the cylinder by acting to urge liquid in the reservoir into the compression chamber through said flow resisting means.
GB-A-1396421 discloses a shock absorber for a motor vehicle. The shock absorber serves to absorb and dissipate the energy from single or limited numbers of successive shocks such as are exerted on vehicles in the event of impact at low speeds so that, up to a predetermined velocity, damage to the chassis of the vehicle does not occur. The disclosed shock absorber comprises a plunger and cylinder unit, the plunger being carried within one tube by a closed end of that one tube and the cylinder comprising a ported tube which is telescopically slidable within the one tube and which is closed at its end further from the closed end of the one tube, the plunger being forced .into the ported tube when a load is applied to the shock absorber whereby liquid is displaced from a compression chamber within the cylinder into a relatively low pressure reservoir through flow resisting means which provide dynamic resistance, wherein the flow resisting means are formed by the ports of the ported tube and the reservoir is formed around the tubes by a radially deformable membrane or resilient bellows which is connected between the two tubes.
According to GB-A-1396421, since upon a compression stroke the streams of damping liquid forced through the throttling ports of the ported tube into the resilient bellows travel at high velocity and consequently impinge with high energy against the internal wall of the resilient bellows, this could with frequent use of the shock absorber cause damage to the bellows and finally cause it to be so badly damaged that it would become unserviceable. With increasing length of stroke even more throttling ports are blanked off, and the energy of the liquid streams passing through the throttling ports which are the last to be blanked off becomes so high that the resilient bellows should desirably be protected in this region. A flange ring encircling and radially spaced from the ported tube and overlapping the ports adjacent to the outer end of the tube, which are the last ports to be blanked off, and around which the adjacent end portion of the resilient bellows is fixedly mounted so that it remains in lining contact with it throughout extension and compression of the shock absorber, serves to protect that end portion of the bellows.
The disclosed shock absorber is a different kind of energy absorber from a buffer designed for industrial use or for use as a railway side buffer, such buffers needing to be suitable for more frequent and perhaps even continuous use and needing to be able to cope with much higher energy impacts.
It is not necessarily from the damaging effects of high energy streams of liquid emerging from the last ports to be blanked off that the bellows needs to be protected. There could be a need for protection from the damaging effects of the streams of liquid that are the first to be blanked off in the event of a high energy impact. Thus it is desirable to provide protection from the damaging effects of the liquid streams that emerge from any or all of the ports of the ported tube.
If the flange ring that provides protection for the adjacent end portion of the bellows were to be extended axially so as to overlap all the ports of the ported tube, the bellows would be liable to be damaged by contact with it before completion of the compression stroke. Also, liquid would be trapped in the inflated toriodal portion of the bellows which would be closed by the flange ring so that the bellows would not function as was intended. Furthermore, arranging for the portion of the bellows that is to be protected to be mounted on the projecting flange ring which it lines means that portion of the bellows material is not available to be inflated for the bellows function and that there is a need to provide a liquid tight seal between the bellows material and the flange as well as between the flange and the ported tube.
We are aware of East German Patent 226632 which discloses a buffer of the kind referred to, wherein the reservoir comprises an annular chamber formed around the plunger by an annular radially deformable membrane which has one of its ends connected to the plunger and its other end connected to the cylinder. The flow restricting means comprise a metering needle which is mounted in a closed end wall of the cylinder and which projects axially towards the plunger, and a metering orifice formed in a blind axial bore formed in the plunger into which a profiled portion of the metering needle projects. Radial passages formed in the plunger provide communication between the axial bore and the annular reservoir chamber formed around the plunger. The resilient means comprise a Ringfeder spring arrangement which surrounds the piston and cylinder unit.